This invention relates to a novel positive type photosensitive resin composition which may be employed for the preparation of a printed circuit board, an integrated circuit or the like. More particularly, it relates to a novel positive type photosensitive resin composition which may be produced easily and which is excellent in compatibility with other resins and is capable of forming a coating film having adhesiveness onto a substrate.
In keeping up with recent progress in the field of electronic equipment, higher density, higher integration and smaller circuit size have been demanded of the printed circuit board as a holder or substrate. Consequently, a substrate surface mounting system, in which small-sized through-holes for electrical connection between the front and reverse substrate sides are formed in the substrate, has been adopted for mounting components on the substrate. The through-holes, which have their inner wall surfaces plated with metal, serve the purpose of interconnecting electrical circuits on the front and back sides of the substrate and securing the components in position.
For producing a printed circuit board having these through-holes and interconnection of a fine line-width by etching, it is necessary to protect a metal plating layer on the inner wall of the through-hole from an etching solution. However, with a method of laminating a dry photosensitive film, which is nowadays employed extensively, since the film thickness is generally as thick as 50 .mu.m, a circuit pattern formed on light exposure and development is not well-defined, so that s fine circuit pattern cannot be formed. Besides, it is difficult to laminate a photosensitive film uniformly on the metal surface, so that the metal plating layer on the inner wall of a particularly small-sized through-hole cannot be protected satisfactorily.
On the other hand, if a resist is formed by an electrodeposition method capable of uniformly coating an etching resist, with the use of a current negative type electrodeposition photoresist consisting essentially of a photocurable resin, the inner part of the through-hole cannot be cured sufficiently because of shortage in the light volume irradiated into the through-holes, such that it becomes difficult to protect the plating metal layer on the inner wall surface against attack by the etching solution. For overcoming the above problems of the prior art, researches into a positive type electrodeposition photoresist, which has its exposed portion dissolved in a developing solution and its non-exposed portion turned into a protective layer and which can be uniformly applied to the substrate by electrodeposition, are currently proceeding, and a variety of proposals have been made. With the positive type photoresist, since the portion exposed to light becomes soluble in a solvent, so that the resist is dissolved and removed, while the portion not exposed to light is non-soluble in the solvent and hence is not removed but is left as a protective layer, it becomes possible to form the protective layer without the necessity of radiating the light to a recessed portion within the through-hole to which the light can be radiated only difficultly.
The above-mentioned positive type photoresist, in which a photosensitive component is a compound containing a quinone diazido group and a developing solution is an alkaline aqueous solution, is attracting attention because of its superior sensitivity and high resolution. If the positive type photoresist containing the quinone diazido group contains a group promoting dissolution in the alkaline aqueous solution and a quinone diazido group in one and the same resin, such photoresist is difficult to purify and hence is not desirable industrially. Therefore, a resin composition is currently employed which is composed of a resin or compound containing a quinone diazido group and a resin capable of promoting dissolution with respect to an alkaline aqueous solution. If the positive type photosensitive resin composition is to be produced by mixing the resin or compound having the quinone diazido group and the resin capable of promoting the dissolution at such a proper ratio as to assure optimum sensitivity, it is crucial to improve compatibility between the two components in order to achieve high resolution.
However, quinone diazido compounds, which may be produced currently on an industrial basis, exhibit only poor compatibility with an alkali-soluble resin, above all, a resin containing carboxylic groups, such as acrylic resin, so that the positive type photoresist solution or the positive type photoresist electrodeposition solution is low in stability and resolution and hence the performance of the resist can not be said to be unobjectionable.